Packaging arrangements employing solder bumps are known. Examples include ball grid arrays (“BGAs”) and chip-scale packages (“CSPs”). By way of illustration, BGAs have a series of solder bumps (or “balls”) typically arranged on the bottom of the package. The solder balls are used to attach the BGA package to a printed wiring board (“PWB”) using a reflow technique. During the reflow process, the solder balls are melted, and upon melting, the solder balls electrically and mechanically join various of the BGA package traces to various of the system PCB traces.
A PWB generally exhibits some degree of flexibility depending on its structural composition and its operating environment, whereas the packages mounted on the PWB remain relatively rigid by comparison. This difference can result in significant mechanical stresses being asserted between the PWB and the package, causing the physical connection between the package and the PWB to fail. An example of a severe failure is when the solder ball is disconnected from a corresponding contact on the PWB, resulting in an interruption of the connection between appropriate contacts of the package and the PWB. Such failures are typically remedied by way of expensive and time-consuming tear down and reassemble of the package and PWB, resulting in undesirable expense and inconvenience to both manufacturer and consumer.
Existing approaches for resolving this problem have a number of drawbacks. For example, the use of expensive rigid boards significantly raises costs. In addition, such rigid boards typically employ insulating layers comprising epoxy and glass, which, among other problems, are difficult to drill, e.g., for forming vias. Consequently, assembly productivity is reduced. Another approach is to increase the size of the solder balls used to connect packages and PWBs. However, increasing the volume of the solder balls between the surface of the package and the PWB can result in bridging adjacent solder balls, thereby undesirably shorting contacts, which can result in malfunctions and/or damage.
Accordingly, there remains a strong need in the art to provide a cost effective and reliable assembly for printed wiring board and packages employing solder joints.